Arrangement and method for continuously supplying electric power to a field device in a technical system

ABSTRACT

An arrangement is described for supplying electrical power to a field device in a process installation which is equipped with a wire-free communication interface without the use of wires. At least one fuel cell having a membrane/electrode block and a fuel tank as well as an electrical energy store are integrated in a housing in the field device, with the fuel cell being equipped with an oxygen reservoir which provides the oxygen that is required for production of electrical energy by oxidation of the fuel in the membrane/electrode block. In addition, the fuel cell is equipped with a water reservoir unit which holds the water which is created during the production of electrical power in the membrane/electrode block by oxidation of the fuel with the oxygen. The fuel cell together with the membrane/electrode block, the fuel tank, the oxygen reservoir and the water reservoir unit form a modular, closed system.

The invention relates to an arrangement for supplying electrical powerto a field device in a process installation which is equipped with awire-free communication interface, without the use of wires, as claimedin the precharacterizing clause of claim 1. The invention also relatesto a method for supplying electrical power to a , field device in aprocess installation without the use of wires, as claimed in theprecharacterizing clause of claim 12.

Field devices which are equipped with a wire-free communicationinterface, for example a GPRS or Bluetooth interface, are known for usein process installations, with appliances such as these having not onlya sensor/actuator unit which includes the actual measurement or controlmodule, a control, data acquisition and processing module and thewire-free communication interface as well, but also a power generationand production unit for supplying power to the field device within ahousing, without the use of wires. A variant of a power generation andproduction unit which uses a fuel cell appears to be particularlyadvantageous in this case. A fuel cell, in which (as is known)electrical power and water are produced by oxidation of a fuel withoxygen in a membrane/electrode block, has an energy density which is atleast 20 times greater than, for example, a lead-acid rechargeablebattery, that is to say a power generation and production unit whichuses a fuel cell can be designed to be considerably more compact and tobe cheaper than a lead-acid rechargeable battery with the same capacity.This is particularly important for supplying electrical power to fielddevices in process installations. DE 201 07 114 U1 describes anarrangement such as this where the fuel is taken directly from a fuelline. In order to ensure a continuous and uninterruptible electricalpower supply to the field device even in the event of the fuel supplybriefly failing, an energy store is provided in the system according toDE 201 07 114, as a temporary store for the electrical energy that isproduced.

Since fuel lines are not available in all application situations, it hasbeen proposed that a fuel reservoir also be provided directly as part ofthe power generation and production unit. DE 199 29 343 describes acorresponding arrangement for supplying electrical power to a largenumber of sensors and/or actuators without the use of wires, with amicro fuel cell with an associated fuel tank being integrated in each ofthe sensors. The required oxygen is obtained from the surrounding air,in the generally normal way for fuel cells that are used at the moment.

An arrangement such as this cannot, of course, be used when the fielddevice is intended to be used in an environment in which no oxygen fromthe air is available. Fields of use such as these may, for example, beflowmeters which are buried in the ground together with a water pipe, orelse when using field devices which have been made suitable forunderwater use for flow, pressure or temperature measurement or forvalve drives for submarine natural-oil supplies.

The efficiency of a conventional fuel cell as known at the moment islimited by the oxygen supply from the surrounding air, which is obtainedby diffusion, and is thus limited. It is desirable to extend thepossible uses of fuel cells in field devices by improving the efficiencyof the fuel cell systems that are used.

The object of the present invention is thus to provide an arrangementfor supplying electrical power to a field device in a processinstallation which is equipped with a wire-free communication interface,without the use of wires, using a fuel cell with a fuel tank and anenergy store for supplying electrical power, which avoids thedisadvantages of the known arrangements and, in particular, can also beused in environments without any oxygen from the air, and to develop amethod for supplying electrical power to a field device in a processinstallation which is equipped with a wire-free communication interface,without the use of wires.

With regard to the arrangement, the object is achieved by thecharacterizing features of claim 1, and with regard to the method it isachieved by the characterizing features of claim 13.

Thus, according to the invention, the fuel cell is equipped with anoxygen reservoir which provides the oxygen that is required forproduction of electrical energy by oxidation of the fuel in the fuelcell. Furthermore, the fuel cell is equipped with a water reservoir unitwhich holds the water which is created during the production ofelectrical power in the membrane/electrode block by oxidation of thefuel with the oxygen. In particular, the fuel cell together with themembrane/electrode block, the fuel tank, the oxygen reservoir and thewater reservoir unit form a closed system.

In one particularly advantageous refinement of the invention, the oxygenin the oxygen reservoir is pressurized. This is because the oxygen canthen be supplied to the membrane/electrode block at an increasedpressure, which improves the efficiency of the fuel cell.

It is highly advantageous to be able to regulate the pressure of thefuel at the interface between the fuel tank and the fuel cell by meansof a fuel pressure regulating device and/or to be able to regulate thepressure of the oxygen at the interface between the oxygen reservoir andthe fuel cell by means of an oxygen pressure regulating device. In thiscase, the fuel and/or oxygen pressure regulating devices may bemechanical pressure regulating valves, membrane pressure regulators orelectronic pressure regulators.

Arrangements designed according to the invention are distinguished inthat the power of the fuel cell can be adjusted and/or regulated, withthe fuel pressure and/or the oxygen pressure being the manipulatedvariables.

A further advantageous refinement option for the invention provides thatthe water reservoir unit is a water tank which is connected to themembrane/electrode block.

In another highly advantageous refinement, the fuel cell is equippedwith at least one current sensor for measurement of the electric currentproduced by it, or with an energy measurement device for measurement ofthe electrical energy produced by it.

However, one advantageous refinement of the invention can also becharacterized in that the fuel cell together with the membrane/electrodeblock, the fuel tank, the oxygen reservoir, the water reservoir unit,the fuel pressure regulating device and the oxygen pressure regulatingdevice which may be provided, the at least one current sensor or the atleast one energy measurement device are in the form of a modular, closedsystem, with the membrane/electrode block, the fuel tank, the oxygenreservoir, the water reservoir unit, the fuel and/or oxygen pressureregulating device or devices and the at least one current sensor or theat least one energy measurement device being individually replaceablemodules and having the capability to be connected to one another and/orto the fuel cell by detachable connecting apparatuses.

A further advantageous refinement option for the invention provides thatthe membrane/electrode block together with the fuel tank, the oxygenreservoir, the water reservoir unit, the fuel and/or oxygen pressureregulating device or devices and the current sensor or sensors or energymeasurement devices are integrated in a pressure-resistant housing. Forsafety reasons, a pressure-relief valve can advantageously be installedin the pressure-resistant housing in this case; a pressure-relief valvecan also be installed in the housing of the field device.

It is particularly advantageous to have the capability to regulate thefuel cell power by means of a micro-processor which is integrated in thefield device or by means of a controller, with the microprocessor orcontroller being connected at least to the current sensor and/or to theenergy measurement device for measurement of the electric current whichis produced by the fuel cell or of the electrical energy which isproduced by it, and being connected to the fuel and/or oxygen pressureregulating device or devices.

The microprocessor or controller can also be connected to the wire-freecommunication interface of the field device, so that information aboutthe state of the fuel cell and/or details about the amount of electricalenergy produced can be interchanged by the microprocessor or controllervia the wire-free communication interface with a central unit which islocated outside the field device.

Overall, an, apparatus according to the invention has the advantage thatthis has resulted in a field device with a wire-free communicationdevice with a completely autonomous electrical power supply. The fielddevice can thus be used in environments without any oxygen from the air.The energy density of the electrical power supply is approximately 20times greater than that of lead-acid rechargeable batteries as arecurrently used in field devices. with a wire-free communication device,and its energy density is about 3 to 6 times greater than that oflithium-ion rechargeable batteries. The modular design of thearrangement according to the invention allows the field device to beinstalled and maintained highly cost-effectively, since all that isrequired for maintenance is to replace prefabricated modules, such asthe fuel tank or the oxygen tank.

In principle, the advantages mentioned above apply to all types of fielddevices, but in particular to field devices with an overall power demandof a few milliwatts.

With regard to the method for supplying electrical power to a fielddevice in a process installation which is equipped with a wire-freecommunication interface, without the use of wires, the essence of theinvention is that the oxygen which is required for production ofelectrical power by oxidation of the fuel in the membrane/electrodeblock is provided from an oxygen reservoir with which the fuel cell isequipped, and that the water which is created during the production ofelectrical power in the membrane/electrode block by oxidation of thefuel with the oxygen is held in a water reservoir unit.

The pressure of the fuel at the interface between the fuel tank and themembrane/electrode block is regulated by means of a fuel pressureregulating device, and the pressure of the oxygen at the interfacebetween the oxygen reservoir and the membrane/electrode block isregulated by means of an oxygen pressure regulating device.

The electric current which is produced by the fuel cell is measured bymeans of a current sensor; however, the electrical energy which isproduced by the fuel cell can also be measured by means of an energymeasurement device.

The power from the fuel cell is regulated, with the signal from the atleast one current sensor or the signal from the at least one energymeasurement device being the controlled variable, and the fuel pressureand/or the oxygen pressure being the manipulated variables.

The water which is created during the production of electrical power inthe fuel cell on the basis of the oxidation of the fuel with the oxygenis supplied via a valve and a water pump to the water reservoir unit,and at least some of it can also be passed back once again from there asrequired to the membrane/electrode block. However, it would also bepossible for the water that is created just to be collected within thepressure-resistant housing although, in this case, it would, of course,no longer be possible to feed even part of the water back into themembrane/electrode block.

In particular, it is advantageous for the fuel cell power to beregulated by means of a microprocessor which is integrated in the fielddevice, or by means of a controller, and for the microprocessor orcontroller to be connected at least to the current sensor and/or to theenergy measurement device for measurement of the electric current thatis produced by the fuel cell, or of the electrical energy which isproduced by it, and to the fuel and/or oxygen pressure measurementdevice or devices. In this case, the microprocessor or controller isadvantageously connected to the wire-free communication interface of thefield device such that information about the state of the fuel celland/or details about the amount of electrical power produced can beinterchanged by the microprocessor or controller via the wire-freecommunication interface with a central unit which is located outside thefield device.

Further advantageous refinements and improvements of the invention, aswell as further advantages, can be found in the dependent claims.

The invention as well as further advantageous refinements andimprovements of the invention will be explained and described in moredetail with reference to the drawing, which illustrates one exemplaryembodiment of the invention.

As an exemplary embodiment, the single figure shows an arrangement forsupplying power to a field device 10 without the use of wires, whichfield device 10 in the example illustrated here is an analysis appliancefor analysis of the composition of a process medium which is carried ina pipeline 1 of a technical process and is represented by an arrow 1 ain the figure. The field device 10 is surrounded by a housing 11 and hasa sensor/actuator unit 6 which has the measurement or control module 3(in this case also referred to as analysis modules in the followingtext), a control, data acquisition and processing module 4, and thewire-free communication interface 5 as well and a sampling line 2, bymeans of which a sample is taken from the process medium la flowingthrough the pipeline 1, and is supplied to the sensor/actuator unit 6.Depending on the process medium and the objective, the analysis module 3may be an apparatus for automatic water or gas analysis, for example aprocess gas chromatograph, a process photometer, a process pH meter, aconductivity analyzer, a process nitrate analyzer, a process oxygenanalyzer, or the like. The control, data acquisition and processing unit4 monitors the sequence of the measurement process in the analysismodule 3, controls the recording of measurement data and, if required,carries out measurement data preprocessing. Data is interchanged bymeans of the wire-free communication interface 5 between the fielddevice 10 and a central unit (which is not illustrated here). The datainterchange is represented by the bidirectional arrow 5 a.

The fuel cell 14 has a membrane/electrode block 15, a fuel tank 18, anoxygen reservoir 16 and a water reservoir unit 20. A current sensor 26and an energy measurement device 28 are installed at the interfacebetween the fuel cell 14 and the sensor/actuator unit 6. While thecurrent sensor 26 measures the amount of current which is interchangedbetween the fuel cell 14 and the sensor/actuator unit 6, the energymeasurement device 28 additionally contains an integration apparatus, bymeans of which a value for the electrical energy is determined from thetime profile of the current. It would also be possible to provide justthe current sensor 26 or just the energy measurement device 28.

Furthermore, an energy store 24 is installed at the interface betweenthe fuel cell 14 and the sensor/actuator unit 6, as a temporary storefor the electrical energy that is produced.

In the exemplary embodiment described here, hydrogen is used as thefuel. The membrane/electrode block 15 may be a polymermembrane/electrode block which is known per se and which can also bemanufactured using micro-technical methods that are known per se, forthe purpose of volume reduction and cost-saving. The fuel tank 18 is,for example, a pressurized hydrogen tank, which is known per se, or ametal hydride hydrogen reservoir, which is likewise known per se.

Alternatively, it is also possible to use a liquid fuel such as methanolor ethanol, with the fuel tank 18 then being a tank that is suitable forthis purpose.

In the illustrated example, the oxygen reservoir 16 is a pressurizedoxygen tank. The oxygen is thus pressurized in the oxygen reservoir 16.

The water reservoir unit 20 is a water tank, which is preceded by avalve 42.

The fuel tank 18, the oxygen reservoir and the water reservoir unit 20are connected to the membrane/electrode block 15 via respectivelysuitable interfaces.

The interface between the fuel tank 18 and the membrane/electrode block15 is a fuel pressure regulating device 41 with an integrated valve. Itwould also be possible to provide the valve separately from the fuelpressure regulating device. In a corresponding manner, the interfacebetween the oxygen reservoir 16 and the membrane/electrode block 15 isformed by an oxygen pressure regulating device 40 with an integratedvalve.

A bidirectional water feed device 43 is arranged at the interfacebetween the water reservoir unit 20 and the membrane/electrode block 15,and cannot only pump water from the water reservoir unit 20 to themembrane/electrode block 15, but can also pump water from themembrane/electrode block 15 into the water reservoir unit 20.

The fuel cell 14 together with the membrane/electrode block 15, the fueltank 18, the oxygen reservoir 16, the water reservoir unit 20, the fueland oxygen pressure regulating devices 40, 41 and the current sensor 26as well as the energy measurement device 28 are in the form of amodular, closed system. This means that the membrane/electrode block 15,the fuel tank 18, the oxygen reservoir 16, the water reservoir unit 20,the hydrogen and oxygen pressure regulating devices 40, 41, the currentsensor 26 and the energy measurement device 28 are individuallyreplaceable modules which can be connected to one another by means ofdetachable connecting apparatuses 30, 31, 32, 33, 34, 35, 36, 37, 38, 39and can be replaced.

The modular configuration in particular offers the advantage of simpleand cost-effective installation and maintenance by replacement of amodule which may be defective by a new module.

A microprocessor or controller 22 is also integrated in the field device10 and is connected to the current sensor 26, to the energy measurementdevice 28, to the hydrogen and/or oxygen pressure regulating device ordevices 40, 41, and to the valve 42. The microprocessor or controller isalso connected to the sensor/actuator unit 6 and thus to the wire-freecommunication interface 5, to the analysis module 3 and to the waterpump 43. This allows information about the state of the fuel cell 14and/or about the electrical energy that is produced to be interchangedfrom the microprocessor or controller via the wire-free communicationinterface with a central unit which is located outside the field device.In this way, the microprocessor or controller 22 can also regulate allthe functional processes within the fuel cell 14.

LIST OF REFERENCE SYMBOLS

-   1 Pipeline-   1 a Process medium-   2 Sampling line-   3 Measurement or control module, also referred to as an analysis    module-   4 Control, data acquisition and processing module-   5 Wire-free communication interface-   5 a Direction arrow-   6 Sensor/actuator unit-   10 Field device-   11 Housing-   12 Power generation and production unit-   14 Fuel cell-   16 Oxygen reservoir-   18 Fuel tank-   20 Water reservoir unit-   22 Microprocessor-   24 Energy store-   26 Current sensor-   28 Energy measurement device-   30 Connecting apparatus-   31 Connecting apparatus-   32 Connecting apparatus-   33 Connecting apparatus-   34 Connecting apparatus-   35 Connecting apparatus-   36 Connecting apparatus-   40 Oxygen pressure regulating device-   41 Fuel pressure regulating device-   42 Valve-   43 Water pump

1. An arrangement for supplying electrical power to a field device in aprocess installation which is equipped with a wire-free communicationinterface, without the use of wires, with at least one fuel cell havinga membrane/electrode block and a fuel tank as well as an electricalenergy store being integrated in a housing in the field device,comprising: a fuel cell equipped with an oxygen reservoir which providesoxygen that is required for production of electrical energy by oxidationof the fuel in the membrane/electrode block, a water reservoir unitwhich holds water which is created during the production of electricalpower in the membrane/electrode block by oxidation of the fuel with theoxygen, and wherein the fuel cell together with the membrane/electrodeblock, a fuel tank, the oxygen reservoir and the water reservoir unitform a closed system.
 2. The arrangement as claimed in claim 1, whereinthe oxygen in the oxygen reservoir is pressurized.
 3. The arrangement asclaimed in claim 1, wherein the pressure of the fuel at the interfacebetween the fuel tank and the membrane/electrode block can be regulatedby means of a fuel pressure regulating device and/or the pressure ofoxygen at an interface between the oxygen reservoir and themembrane/electrode block can be regulated by means of an oxygen pressureregulating device.
 4. The arrangement as claimed in claim 3, wherein thefuel and/or oxygen pressure regulating devices are mechanical pressureregulating valves, membrane pressure regulators or electronic pressureregulators.
 5. The arrangement as claimed in claim 1, wherein the powerof the fuel cell can be adjusted and/or regulated, with the fuelpressure and/or the oxygen pressure being the manipulated variables. 6.The arrangement as claimed in claim 1, wherein the water reservoir unitis a water tank which is connected to the membrane/electrode block. 7.The arrangement as claimed in claim 1, wherein the fuel cell is equippedwith at least one current sensor for measurement of the electric currentproduced by it, or with an energy measurement device for measurement ofthe electrical energy produced by it.
 8. The arrangement as claimed inclaim 7, wherein the fuel cell together with the membrane/electrodeblock, the fuel tank, the oxygen reservoir, the water reservoir unit,the fuel pressure regulating device and the oxygen pressure regulatingdevice which may be provided, the at least one current sensor or the atleast one energy measurement device are formed as a modular, closedsystem, with the membrane/electrode block, the fuel tank, the oxygenreservoir, the water reservoir unit, the fuel and/or oxygen pressureregulating device or devices and the at least one current sensor or theat least one energy measurement device being individually replaceablemodules and having the capability to be connected to one another bydetachable connecting apparatuses.
 9. The arrangement as claimed inclaim 8, wherein the membrane/electrode block together with the fueltank, the oxygen reservoir, the water reservoir unit, the fuel and/oroxygen pressure regulating device or devices and the current sensor orsensors or energy measurement devices are integrated in apressure-resistant housing.
 10. The arrangement as claimed in claim 9,wherein a pressure-relief valve is installed in the pressure-resistanthousing and/or in the appliance housing.
 11. The arrangement as claimedin claim 7, wherein the fuel cell power can be regulated by means of amicroprocessor which is integrated in the field device or by means of acontroller, with the microprocessor or controller being connected atleast to the current sensor and/or to the energy measurement device formeasurement of the electric current which is produced by the fuel cellor of the electrical energy which is produced by it, and being connectedto the fuel and/or oxygen pressure regulating device or devices.
 12. Thearrangement as claimed in claim 11, wherein the microprocessor orcontroller is connected to the wire-free communication interface of thefield device, and information about a state of the fuel cell and/orelectrical energy produced can be interchanged by the microprocessor orcontroller via the wire-free communication interface with a central unitwhich is located outside the field device.
 13. A method for supplyingelectrical power to a field device in a process installation which isequipped with a wire-free communication interface, without the use ofwires, with at least one fuel cell having a membrane/electrode block anda fuel tank as well as an electrical energy store being integrated inthe field device, comprising: providing oxygen which is required forproduction of electrical power by oxidation of the fuel in themembrane/electrode block from an oxygen reservoir with which the fuelcell is equipped, and holding in a water reservoir unit, of the fuelcell, water which is created during production of electrical power inthe membrane/electrode block by oxidation of the fuel with the oxygen.14. The method as claimed in claim 13, comprising: regulating thepressure of the fuel at the interface between the fuel tank and themembrane/electrode block by means of a fuel pressure regulating deviceand/or regulating the pressure of the oxygen at the interface betweenthe oxygen reservoir and the membrane/electrode block by means of anoxygen pressure regulating device.
 15. The method as claimed in oneclaim 13, comprising: measuring electric current which is produced bythe fuel cell by means of a current sensor, and/or measuring theelectrical energy which is produced by the fuel cell is measured bymeans of an energy measurement device.
 16. The method as claimed inclaim 15, comprising: adjusting and/or regulating the fuel cell, withthe fuel pressure and/or the oxygen pressure being the manipulatedvariables.
 17. The method as claimed in claim 16, comprising: regulatingpower of the fuel cell, with the signal from the at least one currentsensor or the signal from the at least one energy measurement devicebeing the controlled variable.
 18. The method as claimed in claim 13,comprising supplying water which is created during the production ofelectrical power in the membrane/electrode block on the basis of theoxidation of the fuel with the oxygen via a valve and a water pump tothe water reservoir unit, and passing at least some of it back onceagain from there as required to the membrane/electrode block.
 19. Themethod as claimed in claim 13 comprising: collecting water which iscreated during the production of electrical power in themembrane/electrode block on the basis of the oxidation of the fuel withthe oxygen within the pressure-resistant housing.
 20. The method asclaimed in claim 13 comprising regulating fuel cell power by means of amicroprocessor which is integrated in the field device, or by means of acontroller.
 21. The method as claimed in claim 20, wherein themicroprocessor or controller connected to the wire-free communicationinterface of the field device.